Why is my air conditioner freezing up?

Your air conditioner is likely freezing up due to restricted airflow or low refrigerant levels, both of which cause the evaporator coil to get too cold and ice over.

Restricted airflow is the most common culprit. When your AC can't pull enough warm air across the evaporator coil, the coil temperature drops below freezing and ice forms. This typically happens when your air filter is severely clogged, blocking airflow to the system. Other airflow issues include closed or blocked vents, dirty evaporator coils, or problems with the blower fan motor.

Low refrigerant levels from a leak can also cause freezing. When refrigerant is low, the remaining refrigerant expands too much in the evaporator coil, causing extremely cold temperatures that freeze moisture in the air. You might notice reduced cooling performance along with the ice buildup if this is the issue.

In Ottawa's climate, freezing can also occur when you run your AC during cooler weather (below 15°C/60°F). Most residential air conditioners aren't designed to operate efficiently in cool temperatures and can freeze up even under normal conditions.

Immediate steps: Turn off your AC immediately and let all ice melt completely before restarting - this usually takes 2-4 hours. Check and replace your air filter if it's dirty, and ensure all vents are open and unobstructed.

When to call a professional: If the problem persists after addressing airflow issues, you likely have a refrigerant leak or mechanical problem that requires a licensed HVAC technician. In Ontario, only licensed technicians can handle refrigerant, and continuing to run a frozen AC can damage the compressor - an expensive repair typically costing $1,500-$3,000 in the Ottawa market.

For a proper diagnosis of your AC freezing issue, Ottawa HVAC Pro offers comprehensive system inspections to identify and resolve the root cause.